1. Field of the Invention
The present invention generally relates to a method and a device for driving a display, and particularly relates to a method and a device which are suitable for driving a plasma display panel (hereinafter referred to simply as PDP).
2. Description of the Related Art
There is a PDP which performs surface discharge. In such a PDP, all the pixels of the display screen simultaneously glow in accordance with data to be displayed. A PDP that performs surface discharge includes a pair of electrodes inside a front glass panel, and contains rare gas inside the sealed space. As a voltage is applied between the electrodes, surface discharge is observed between the surfaces of the electrodes having a dielectric layer and a protection layer formed thereon. This discharge generates ultraviolet light. An inner surface of a rear glass panel is provided with fluorescent materials corresponding to three primary colors, i.e., red (R), green (G), and blue (B). The ultraviolet light excites the fluorescent materials such that these materials emit light to achieve color display. Here, fluorescent materials for R, G, and B are provided for each pixel of the display screen.
Since the PDP is a light emitting device, it provides a visually better display quality. Also, the PDP can provide a large display screen with a thin bulk. All of these factors make the PDP an attractive display device of the next generation to replace the CRT device. A PDP of a surface AC (alternating current) discharge type is especially suitable for a large display screen, and is expected to be a main display device to be used along with high-definition digital television technology. In an information age which is further advancing as can be seen in development of the Internet, a display device is expected to be an integrated part of the multi-media technology, which combines video media such as television with information media such as personal computers.
In such application, HDTV broadcasting utilizing more than 1,000 scan lines or DVD media may serve as a video source. As far as displaying of information is concerned, an effort to attain finer display details has got to a point where we have an SXGA of 1280-x-1024 dots, and a display format is ever more diversified. Against this background, a display device which can cope with various formats and has more than 1000 scan lines is necessary.
FIGS. 1 and 2 are a plan view and a cross-sectional view, respectively, of a PDP disclosed in Japanese Laid-Open Patent Application No. 9-160525 by the applicant of the present application. This PDP is driven based on an ALIS (alternate lighting of surface) method. In FIGS. 1 and 2, a PDP 1 includes a front glass panel 3, discharge sustaining electrodes X1, Y1, X2, Y2, X3, and Y3 provided in parallel on the front glass panel 3, a rear glass panel 4, address electrodes A1 through A4 provided on the rear glass panel 4 in perpendicular to the discharge sustaining electrodes, barrier ribs 2 which shield discharge spaces from each other by extending in parallel to the address electrodes, fluorescent material 5 applied on the rear glass panel 4, and a gas contained between the front glass panel 3 and the rear glass panel 4 for facilitating discharge.
As shown in FIG. 2, a single discharge cell is defined by two discharge sustaining electrodes (e.g, X1 and Y1) and an address electrode (e.g., A1). A discharge sustaining electrode can maintain discharge with adjacent discharge sustaining electrodes on either side thereof, so that all the gaps between the discharge sustaining electrodes shown in FIG. 1, i.e., lines L1 through L5, serve as display lines. For example, the discharge sustaining electrodes X1 and Y1 together create the display line L1, and the discharge sustaining electrodes Y1 and X2 together create the display line L2.
In FIG. 2, a voltage is applied between the discharge sustaining electrodes X1 and Y1 to generate discharge in a discharge area D1, and a voltage is applied between the discharge sustaining electrodes Y1 and X2 to generate discharge in a discharge area D2. By the same token, a voltage is applied between the discharge sustaining electrodes X2 and Y2 to generate discharge in a discharge area D3. In this manner, a single discharge sustaining electrode is used for generating display lines on either side thereof. This configuration makes it possible to reduce the number of discharge sustaining electrodes, thereby achieving a finer display pitch and reducing the number of driver circuits for driving the discharge sustaining electrodes.
FIG. 3 is an illustrative drawing showing a configuration of a frame which the PDP displays.
One frame is comprised of a first field and a second field. A field frequency is 60 Hz, so that the field cycle is 16.6 msec. The first field displays odd-number display lines L1, L3, L5, and so on, and the second field displays even-number display lines L2, L4, L6, and so on, thereby displaying all the display lines. Namely, the display scheme is similar to interlace scanning of a CRT device. Each field is comprised of first through eighth sub-field, each of which has a different luminance ratio, i.e., a different discharge period (the number of discharges). The sub-fields are selectively lighted up in accordance with display data so as to represent a different luminance level of each pixel. Each sub-filed includes a reset period for making uniform the conditions of discharge cells as the conditions of discharge cells depend on the way the immediately preceding sub-field was displayed. Each sub-field further includes an address period for writing new display data and a discharge sustaining period for displaying the display data via discharge sustaining operations.
FIGS. 4A through 4E are illustrative drawings showing signal forms of a given sub-field of the first field in a PDP device. As shown in FIGS. 4B and 4D, a reset pulse having a peak voltage Vw, which is greater than a voltage to generate discharge, is applied to all the X-series discharge electrodes during the reset period. This generates first discharge at all the lines L1 through L5. As a result, each discharge cell has a wall voltage developed based on positive ions or electrons.
After the reset pulse, the wall voltage generates a second discharge. Since there is no voltage differential between the discharge electrodes at this time, positive ions and electrons generated by the discharge end up being connected to each other in the discharge space, resulting in disappearance of the wall voltage. This discharge works to make the conditions of all the discharge cells uniform.
During the address period, as shown in FIGS. 4C and 4E, the discharge sustaining electrodes Y1 and Y2 in this order receive a scan pulse, which changes from a voltage xe2x88x92Vc to a voltage xe2x88x92Vy. At the same time, scan pulses having a peak voltage Va are supplied to the address electrodes in accordance with the display data, thereby effecting discharge. When this happens, the discharge sustaining electrode X1 forming a pair with the discharge sustaining electrode Y1 for display in the first field receives a pulse having a voltage Vx, so that the discharge generated between the address electrodes and the discharge sustaining electrode Y1 is shifted to a space between the discharge sustaining electrodes X1 and Y1.
This generates wall charge necessary for maintaining the discharge in the space between the discharge sustaining electrodes X1 and Y1. Since the discharge sustaining electrode X2 forming a line which does not display at the same timing with the discharge sustaining electrode X1 receives 0 V as shown in FIG. 4D, spreading of the discharge area toward the discharge sustaining electrode X2 is prevented.
When the scan pulse having the voltage xe2x88x92Vy is applied to the discharge sustaining electrode Y2, the discharge sustaining electrode X2 forming a display pair with the discharge sustaining electrode Y2 receives a pulse having the voltage Vx. At this time, the discharge sustaining electrode X3 receives 0 V. In this manner, scan pulses are successively applied to the Y-series discharge sustaining electrodes, thereby effecting address discharge with respect to all the odd-number display lines of the display screen.
In the discharge sustaining period, sustaining pulses are applied to the X-series discharge electrodes and the Y-series discharge electrodes in turn. The sustaining pulses are adjusted to have such a phase that a voltage difference between discharge electrodes forming a pair for a non-display line is always zero. In this manner, discharge at the non-display line is avoided. For example, the discharge electrodes X1 and Y1 forming a pair for displaying a line in the first field receive respective sustaining pulses having different phases, while the discharge electrodes X2 and Y1 forming a pair for a non-displayed line in the first field receive respective sustaining pulses having the same phase. In this manner, one sub-field is displayed.
In the same fashion, all the even-number lines are displayed in the second field. FIGS. 5A through 5E are illustrative drawings showing signal forms of a given sub-field of the second field. FIGS. 5A through 5E differ from FIGS. 4A through 4E in that the signal form of the discharge electrode X1 shown in FIG. 5B and the signal form of the discharge electrode X2 shown in FIG. 5D are exchanged. In this manner, a voltage is applied between the discharge electrodes which form a pair across even-number lines during the address period and the discharge sustaining period.
Displaying of the first field and displaying of the second field are performed one after the other so as to present a new image in every one frame (33 msec). This configuration can easily implement more than 1000 display lines on a display device.
In related-art devices, interlace scanning similar to that of the conventional television signal is employed. This may lead to generation of flicker, depending on what is displayed on the screen.
FIG. 6 is an illustrative drawing for explaining generation of flicker.
A situation in which the display line L3 alone is lighted up in FIG. 6 is taken as an example. The display line L3 is an odd-number line, and, thus, is lighted up in the first field. During the second field, the display line L3 is not lit up since only the even-number lines are lighted up in the second field. Accordingly, it is the first field of the next frame when the display line L3 glows again. In this case, a display interval is 33 msec. In general, human vision cannot recognize a change in light intensity when the light intensity changes at intervals shorter than 20 msec, i.e., when the light intensity changes with a frequency exceeding 50 Hz. When the light intensity changes at intervals longer than 20 msec however, such a change is recognized as flashing on/off. Because of such nature of human vision, the displaying of the line L3 described above is registered as conspicuous flicker.
In video images such as those of television broadcasting, no display pattern includes a single isolated flashing line, so that flicker, if any, may be present only within a tolerable level. When computer-related data is displayed by personal computers, however, small letters and drawings may be displayed, which may result in apparent flickering.
Accordingly, there is a need for a method and a device for driving a display which can prevent generation of flickering regardless of what is displayed on the screen.
Accordingly, it is a general object of the present invention to provide a method and a device for driving a display which can satisfy the need described above.
It is another and more specific object of the present invention to provide a method and a device for driving a display which can prevent generation of flickering regardless of what is displayed on the screen.
In order to achieve the above objects according to the present invention, a method of displaying display data on a plasma display panel which displays odd-number lines in a plurality of sub-fields and even-number lines in a plurality of sub-fields includes the steps of checking whether the display data is computer-related data or video data, displaying odd-number lines in a predetermined number of sub-fields during a given vertical scan cycle and even-number lines in the predetermined number of sub-fields during another vertical scan cycle if the display data is video data, and displaying odd-number lines in half the predetermined number of sub-fields and even-number lines in the remaining half of the predetermined number of sub-fields in each vertical scan cycle if the display data is computer-related data.
According to the method described above, the video data is displayed in such a conventional interlacing fashion that the odd-number lines are displayed in a predetermined number of sub-fields during a given vertical scan cycle, and even-number lines are displayed in the predetermined number of sub-fields during another vertical scan cycle. On the other hand, the computer-related data is displayed by displaying odd-number lines in half the predetermined number of sub-fields and even-number lines in the remaining half of the predetermined number of sub-fields in each vertical scan cycle, so that displaying of the odd-number lines and the displaying of the even-number lines are performed in turn within a single vertical scan period. This configuration insures that while a given line of the video data is lighted up in every other vertical scan cycle, a given line of the computer-related data is lighted up in every vertical scan cycle. Because of a shorter field interval for the computer-related data, no flicker is observed regardless of the contents of the computer-related data.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.